Currently there are many applications which are susceptible to computer processing including images of one or more planar arrays of pixels. These field may include video, radar, multispectral and sonar data. Typically the planar array of pixels consists of digitally sampled and quantized image data. Each of these pixels in the pixel array thus has a pixel value selected from among a predetermined set of possible values.
In processing these image arrays of pixels, it is often desirable to extract information from the pixel array defining and cataloging which pixels have predetermined pixel values or ranges of values, or which pixels have pixel values of interest. Many cases of image manipulation such as machine vision systems require such defining and cataloging. This cataloging allows direct access to pixels within the image array according to their pixel values rather than according to their location within the image. This process can be understood as a transformation from image-domain or "iconic" processing to symbolic-domain processing. Such symbolic-domain processing is often employed in artificial intelligence systems. Such artificial intelligence systems are particularly useful in the processing of such image arrays. In addition, it is often useful to have a histogram of the number of occurrences of the particular pixel values or ranges of pixel values.
The image data in the planar array of pixels is normally stored, processed and transferred in a regular raster-scan sequence. Such a raster-scan sequence involves recall of the image array of pixels by rows in a regular sequence covering the entire array. It is believed that the process to sequentially interrogate, compose and catalog every pixel of a high-resolution image with a conventional general purpose computer would be extremely time consuming. Such high-resolution images may include pixel arrays of 1,000 by 1,000 pixels or more, thus including more than 1,000,000 pixels.
In view of these factors, it is therefore desirable to be able to construct a directory of the pixel locations within a planar array of pixels which have each of the possible pixel values at a rate equal to the rate at which the pixels may be supplied by available sensor image or data transmission paths. In this regard, it is considered desirable to be able to generate this catalog from the raster-scan data of the entire image. In addition it would also be desirable to simultaneously construct a histogram of all possible pixel values. Such a histogram would permit an analysis of the distribution of the values within the image.